1. Field of the Invention
The present invention relates to a thin film formation apparatus for depositing a thin film of ferroelectric material or the like on a substrate and to a method of forming a thin film using the apparatus.
2. Description of the Background Art
[Background Art of Infrared Detecting Element]
Objects and human bodies at room temperature radiate infrared rays (heat rays) of approximately 10 xcexcm in wavelength which can be measured to detect the presence of them and obtain temperature information without contact. This infrared detection is applied to various uses like automatic door, intruder alarm, cooking monitor of microwave oven, chemical measurement, and the like.
The key device of prime importance for such measurement is an infrared sensor. There are generally two types of infrared sensors, i.e., quantum infrared sensor and thermal infrared sensor.
The quantum infrared sensor is highly sensitive and excellent in sensing ability while it requires cooling resulting in increase in size of the entire device and thus has a problem in practical use. On the other hand, the thermal infrared sensor is somewhat inferior to the quantum infrared sensor in terms of sensitivity while it is appropriate for practical use because of its advantage that operation at room temperature is possible.
Accordingly, various thermal infrared sensors have been proposed including those utilizing pyroelectric effect, resistance bolometer, dielectric bolometer, thermopile, Golay cell, and the like. For example, an infrared image sensor using the pyroelectric effect is disclosed in Proc. 8th IEEE Int. Symp. Appl. Ferroelectronics (1992), pp. 1-10 (xe2x80x9cPYROELECTRIC IMAGINGxe2x80x9d by Bernard M. Kulwicki et al.).
In particular, the dielectric bolometer which applies electric field to detect the change of dielectric constant with respect to temperature has a higher sensitivity than those of other sensors and it requires no chopper. Because of these excellent features, the dielectric bolometers are considered prospective in terms of practical use.
Further, an advanced infrared sensing is expected that is applied to infrared image sensors (thermography) capable of providing temperature distribution of objects and scenery without contact.
[Background Art of Ferroelectric Material for Infrared Detecting Element]
In order to enhance the performance of an infrared detecting element used for the infrared image sensors and the like mentioned above, it is necessary that the material constituting the infrared detecting element has a high sensing sensitivity.
In other words, if a pyroelectric (PE) bolometer utilizing pyroelectric effect is used as an infrared sensor, the pyroelectric coefficient must be large at about room temperature. If the dielectric bolometer (DB) explained above is used as an infrared sensor, the change of dielectric constant with respect to temperature must be great at about room temperature.
Materials of importance for these infrared detecting elements include (Ba0.75Sr0.25) TiO3 (hereinafter abbreviated as BST) and ferroelectric SBN (strontium barium niobate, Sr1xc2x7xBaxNb2O6, 0.25xe2x89xa6xxe2x89xa60.75) crystal having tetragonal tungsten-bronze structure (hereinafter abbreviated as SBN).
SBN particularly exhibits considerably excellent ferroelectric characteristics and the highest pyroelectric coefficient. Moreover, Curie temperature (Tc) of SBN can be varied continuously from 60xc2x0 C. to 250xc2x0 C. by controlling Sr/Nb ratio.
In addition, SBN has a feature of diffusion phase transition. Specifically, ferroelectric phase transition occurs in a relatively wide temperature range near Tc with a considerably high and sharp dielectric peak.
As discussed above, the ferroelectric materials having temperature dependencies of both of polarization and dielectric constant as shown in FIG. 26 are applicable to thermal infrared sensors. The former effect is related to conventional pyroelectric (PE) bolometers and the latter effect is related to dielectric bolometers (DB).
Here, in order to achieve a high sensitivity, the material must have its phase transition temperature (Tc) which is close to a range of measuring temperature and the rate of change of dielectric constant with respect to temperature must be increased.
In actual, Tc value of Sr0.48Ba0.52Nb2O6 is approximately 125xc2x0 C. It is known that the temperature 125xc2x0 C. can be reduced to 60xc2x0 C. by substituting this SBN by 0.5% La2O3. Moreover, SBN material is very stable since the SBN includes no volatile element such as Pb. Mat. Res. Soc. Symp. Proc. Vol. 243, pp. 557-562 (1992) (xe2x80x9cStrontium barium niobate thin films prepared by pulsed laser depositionxe2x80x9d) reports that a thin film of SBN can be grown by means of laser ablation with stoichiometry exactly identical to a target.
Infrared sensors like those described above are arranged in the form of an array to be integrated with a high density so as to produce an infrared image sensor. Then, an array of dielectric ceramic and switching elements like silicon FET (Field Effect Transistor) should be formed on the same semiconductor substrate. It accordingly means that there should be conformity between a process of forming switching elements or the like and a process of forming infrared detecting elements, for example, it is necessary that dielectric ceramic should be formed at low temperature without deteriorated in its characteristics onto a metal electrode formed on a semiconductor substrate.
However, the laser ablation which has conventionally been employed has problems that the deposition temperature is not sufficiently low and that the deposition rate of a ferroelectric thin film is low.
One object of the present invention is to provide a thin film formation apparatus and a thin film formation method by which a thin film of ferroelectric or the like suitable for an infrared detecting element having a high sensing sensitivity can be formed on a substrate.
Another object of the invention is to provide a thin film formation apparatus and a thin film formation method by which a ferroelectric thin film can be manufactured with an enough conformity to a process of forming a device like transistor formed on a semiconductor substrate in an infrared two-dimensional image sensor or the like.
In summary, according to an aspect of the invention, the present invention is a thin film formation apparatus including a vacuum chamber, a target unit, a high energy radiation source, an optical device, a substrate holding unit, an oxidizing gas inlet unit, a heating unit, and a first irradiation unit.
The target unit is provided at a predetermined position in the vacuum chamber and can fix a target containing a film material. The high energy radiation source emits high energy radiation to a surface of the target fixed to the target unit. The optical device concentrates the high energy radiation to the target fixed to the target unit. The substrate holding unit is provided to face the target unit and holds a substrate for depositing thereon a substance ejected from the target by the high energy radiation. The oxidizing gas inlet unit supplies an oxidizing gas into the vacuum chamber so as to oxidize the substance deposited on the substrate. The heating unit heats the substrate in the vacuum chamber. The first irradiation unit irradiates with activation light rays the substrate held by the substrate holding unit.
According to another aspect of the invention, a thin film formation apparatus includes a vacuum chamber, a target unit, a high energy radiation source, an optical device, a substrate holding unit, an oxidizing gas inlet unit, a heating unit, and a first irradiation unit.
The target unit is provided at a predetermined position in the vacuum chamber and can fix a target containing a film material. The high energy radiation source emits high energy radiation to a surface of the target fixed to the target unit. The optical device concentrates the high energy radiation to the target fixed to the target unit. The substrate holding unit is provided to face the target unit and holds a substrate for depositing thereon a substance ejected from the target by the high energy radiation. The oxidizing gas inlet unit supplies an oxidizing gas into the vacuum chamber so as to oxidize the substance deposited on the substrate. The heating unit heats the substrate in the vacuum chamber. The first irradiation unit irradiates with activation light rays the target fixed by the target unit.
According to still another aspect of the invention, a method of forming a thin film includes the steps of: placing a target at a predetermined position in a vacuum chamber, placing a substrate to face the target and decompressing the target and the substrate in the vacuum chamber; heating the substrate in the vacuum chamber; irradiating the substrate with activation light rays; supplying an oxidizing gas into the vacuum chamber for oxidizing a substance to be deposited on the substrate; and emitting high energy radiation to concentrate the radiation to a surface of the target and depositing a substance ejected from the target on the substrate.
According to a further aspect of the invention, a method of forming a thin film includes the steps of: placing a target at a predetermined position in a vacuum chamber, placing a substrate to face the target and decompressing the target and the substrate in the vacuum chamber; heating the substrate in the vacuum chamber; irradiating the target with activation light rays; supplying an oxidizing gas into the vacuum chamber for oxidizing a substance to be deposited on the substrate; and emitting high energy radiation to concentrate the radiation to a surface of the target and depositing a substance ejected from the target on the substrate.
According to a still further aspect of the invention, a method of forming a thin film includes the steps of: applying an organic metal film onto a substrate and annealing the organic metal film in an oxidizing gas ambient to form an inorganic film on the substrate; placing a cylindrical target at a predetermined position in a vacuum chamber, placing the substrate having the inorganic film formed thereon such that the substrate faces the target, and decompressing the target and the substrate in the vacuum chamber; heating the substrate in the vacuum chamber; irradiating the substrate with activation light rays; supplying an oxidizing gas into the vacuum chamber for oxidizing a substance to be deposited on the substrate; and emitting high energy radiation to concentrate the radiation to a surface of the target and depositing a substance ejected from the target on the substrate.
The step of depositing the substance ejected from the target on the substrate includes the steps of rotating the cylindrical target on the central axis of the cylindrical target, and moving the substrate in parallel with the central axis of the cylindrical target.
According to a still further aspect of the invention, a method of forming a thin film includes the steps of: applying an organic metal film onto a substrate and annealing the organic metal film in an oxidizing gas ambient to form an inorganic film on the substrate; placing a cylindrical target at a predetermined position in a vacuum chamber, placing the substrate having the inorganic film formed thereon such that the substrate faces the target, and decompressing the target and the substrate in the vacuum chamber; heating the substrate in the vacuum chamber; irradiating the target with activation light rays; supplying an oxidizing gas into the vacuum chamber for oxidizing a substance to be deposited on the substrate; and emitting high energy radiation to concentrate the radiation to a surface of the target and depositing a substance ejected from the target on the substrate.
The step of depositing the substance ejected from the target on the substrate includes the steps of rotating the cylindrical target on the central axis of the cylindrical target, and moving the substrate in parallel with the central axis of the cylindrical target.
The thin film formation apparatus and method according to the present invention can thus be used to form a ferroelectric thin film so as to achieve an infrared detecting element of a simple structure that is highly sensitive at room temperature. Moreover, such infrared detecting elements can be arranged in a two-dimensional array to achieve an infrared two-dimensional image sensor operating at room temperature with a high sensitivity and highly dense pixels.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.